[Mono-list] Re: IEnumerators

[Serge]

Hello there,

> The best way I can think of
> is to have the original object
> keep a change count.

Exactly, this is how it's implemented in Java, and I really believe it's
done like this in MS implementation. This is so-called "fail-fast
iterators". You may check my implementation of Hashtable for example of
this, which is available still at http://primates.ximian.com/~miguel/tmp/

Also regarding Garrett's Stack implemetation. I think that the Stack's
Enumerator should be implemented this way too.
Garrett, currently you're making the clone of the base stack array. I think
it's a kind of overkill - making the copy to just look at the content. I
believe when specs are talking about snapshots, they actually mean the
version-stamped references, not copys.
Also, I see no reason why synched collection should return synched
enumerator. Maybe I missed some point though. Also, if we assume that we
won't make copys of the content for each Enumerator, and Enumerators are
fail-fast, there is no point to synchronize Enumerator on itself (lock
(this)). Since Enumerators are read-only, this will only add unneeded
overhead.
On the other hand, to provide thread safety for Enumerator, it is imperative
that the client code synchronize iteration loop with the corresponding
_synchorized_ collection returned by Collection.Synchronized(Collection)
method. That is, you obtaining synched collection, then its Enumerator, then
the use of the Enumerator is synchronized on that collection.

Well, re-reading my explanation, I think it's quite unclear :-) Hence,
better refer to the source code. Also looking at JDK docs will help, they
have very detailed description of this, arguably better than that from the
specs/Beta2 docs, notably the terminology there is less confusing.

Also, I think, there ought to be the sort of "skeleton" for all collections
classes, because they share a great deal of functionality and behaviour,
Enumerators for example. Not necessary some code snippet but a set of rules,
like these for Enumerators and corresponding tests-cases to check the
implementation. Any ideas?

--
Sergey